If you do decide to go for a postgraduate course, there are loads of Conservation/Countryside Management MSc's available nowadays - not sure if at Bristol though.
Not wishing to influence any decisions of complete strangers!

- but just wanted to say that I decided in my early teenage years that I wanted to go into conservation and followed it through and have never looked back - I could never do anything else - so even though you are young and still have loads of time to change your mind, if you think conservation is for you then go for it! Some people do know what they want to do early on in their lives - I did and I wasn't wrong